Our objective is to decipher the organization of the primate oculomotor system at the neuronal level. The basic information provided by this research project in the alert monkey will lead to a deeper understanding of the operation of this system in both normal and diseased states in man. Detailed knowledge of this system will also improve the utility of the extensive battery of diagnostic neuroophthalmological tests that have been developed in recent years. The focus of the present project is on the role of the cerebellum and its most important visual input pathways, those from the pontine nuclei, in the control of ocular motility. Specific aims include: 1) To ascertain the role of several small groups of neurons in the dorsal and lateral portion of the pontine nuclei, including nucleus reticularis tegmenti pontis, the mediodorsal, lateral and the dorsolateral pontine nuclei. This is accomplished by the placement of focal chemical lesions (using lidocaine and ibotenic acid) in each of these regions in monkeys previously trained and tested on a wide variety of visual and oculomotor paradigms. Post lesion tests are designed to uncover deficits in the pursuit, optokinetic or saccadic subsystems or in visuovestibular processing. Additional paradigms test for changes in adaptive capability in the pursuit, saccadic, or vestibular systems. 2) To provide a comprehensive picture of the neuronal processing of visual, vestibular, and oculomotor signals within two regions of cerebellar cortex which receive extensive input from the visual portions of pons, but have not previously been studied in the monkey. To accomplish this goal single-neuron recordings will be made in the uvula and the paraflocculus in alert animals. The same paradigms used in Specific aim (1) will be used to characterize the visual and oculomotor properties of both input and cortical neurons in these two cerebellar regions.